The invention provides novel methods for precisely delivering radiation to specific tissues and organ sites, especially the spine. In particular, the invention utilizes image-guided methods (stereotactic radiosurgery [SRS]) to deliver radiation to target sites, especially spinal metastases.
Approximately 25,000 new patients present annually with metastatic tumors to the spine. With the aging population in the U.S. this number is expected to rise significantly over the next two decades. Of these, 60% of the metastases localize to the thoracic-spine, 30% to the lumbar-spine and 10% to the cervical-spine. The lesions cause pathological fracture, pain, deformity and compression of the neural axis or caudal equina. They may be single, but are more often multiple and scattered throughout several levels in different parts of the spine. Many of these patients are candidates for radiation therapy.
Conventional radiation therapy of these lesions involves the treatment of the spine, spinal cord and adjacent tissues. Tolerance doses have been established for the spinal cord at various levels [C-Spine (45-50 Gy) and T-Spine (40-45 Gy)] (based on reviews of clinical experiences). It is generally accepted that the radiation tolerance of blood vessels that supply the spinal cord play an integral role in this complex process. Therefore radio-surgical treatment planning may be designed to limit the radiation dose to the critical blood vessels that supply the spinal cord. FIG. 1 illustrates the locations and relevant positions of the relevant anatomical structures, including the aorta 10, spinal artery 12, intercostal artery 14, vertebral artery 16, medullary artery 18, nerve ganglion/root 20, thecal sac covering the spinal cord 22, Toly triangle 24, transverse process 26, spinous process 28, inferior facet 30, and superior facet 32.
Conventional radiation treatment delivery has several additional drawbacks. First, an excessive volume of otherwise normal hematopoeitic tissue (bone marrow) is irradiated, resulting in compromise of the patient""s hematopoesis (ability to make new blood cells) and thus limiting further treatment options such as chemotherapy. Second, the time frame for delivery is excessive, and results in delays in systemic treatment (chemotherapy). Third, radiation cannot be administered over previously irradiated segments, nor immediately adjacent to previously irradiated segments.
An object of the invention is to alleviate the problems associated with conventional radiation oncology treatments. More specifically, the objects of the invention are: (a) to selectively deliver high dosages of radiation to specific sites near or contained in the spine, especially spinal metastases, by the use of image-guidance methods during radiotherapy; (b) to deliver high dosages of radiation to the spine while avoiding or minimizing the delivery of radiation to adjacent tissues, especially blood vessels in the Toly triangle; (c) to deliver a high single-fraction of radiation by stereotactic radiosurgery (SRS) to a target site, especially spinal metastases.
To achieve these objectives the invention provides an improved method for delivering therapeutic radiation to the spine comprising the following steps:
(i) immobilizing the spine with a novel immobilization bed;
(ii) obtaining a three-dimensional CT image of said immobilized patient which includes an area of the spine that is to be irradiated;
(iii) using said CT image to select an appropriate radiation dosage and volume and delivery protocol; and
(iv) irradiating the spine of said patient according to said selected radiation and dosage protocol.
Preferably, the irradiating step (iv) will further be adjusted to the patient""s respiratory cycle, i.e., by gating the radiation beam on and off at different points in the respiratory cycle.
The present invention provides a novel and improved method for delivery of radiation to areas of the spine, e.g., spinal metastases, that allows for the precise delivery of high dosages of radiation while minimizing or avoiding the delivery of radiation to non-target sites, especially those comprised in the Toly triangle 24.
As discussed above, a significant problem associated with conventional radiation treatment of areas of the spine, especially tumors and metastases, is the fact that conventional delivery methods cannot deliver high dosages of radiation because of the risk of damage to non-target sites, especially critical blood vessels that are comprised in the Toly triangle 24. This is because such blood vessels are only tolerant to low dosages of radiation, e.g., on the order of 12-18 Gy.
This is a problem because low dosages of radiation, even if administered repeatedly, may be insufficient to eradicate the target, typically cancer cells. Also, conventional spinal radiotherapy typically requires a long time frame for delivery and response to radiation, and is moreover complicated by the fact that radiation cannot be administered over previously irradiated segments, nor immediately adjacent to previously irradiated segments of the spine.
The present invention alleviates all of said problems. In particular, the invention provides for the precise delivery of a high dosage of radiation to a target site or sites in the spine, that minimizes the exposure to non-target sites, such as the Toly triangle 24, and which can be effected during a relatively short period, i.e., by the use of stereotactic radiosurgery (SRS).
While the stereotactic radiosurgery technique has been utilized previously to treat intracranial lesions, heretofore it has not been applied to the spine and other extracranial lesions because of the inability to immobilize the spine and provide an accurate localization and three-dimensional planning target volume in a coordinated system that is suitable for both isodose planning and radiation treatment.
The present inventors have alleviated such problems by immobilization of the patient in a device which provides for the immobilization of the spine while a three-dimensional image (CT scan) of the spine is obtained. The CT images with specified coordinate system are utilized to determine appropriate radiation dosages and delivery (e.g., based on establishment of the isocenter and location of the target volume, and specification of target volume and critical structures), and further provide for precise alignment and immobilization of the patient as a therapeutic dosage of radiation is delivered by stereotactic radiosurgery (SRS).
In the present invention, the three-dimensional CT images will preferably be obtained by use of a mobile CT scanner which is set up such that the CT image can be transferred to a radiation treatment planning system that is used to determine optimal radiosurgery dosages and delivery. In preferred embodiments, this will be determined using appropriate software, i.e., BrainLab-Varian micro-MultiLeaf Collimator (mMLC), and the CT image will be obtained using the SpineLab Planar Fiducial system and the BrainLab ExacTrac System of IR markers and stereocameras.
This information will be utilized for inverse treatment planning for IMRT technique, which will take into account radiation sensitive structures, especially those within the Toly triangle. Radiosurgery is effected while the patient""s spine remains immobilized and is precisely aligned in a suitable position for treatment, using the external coordinate system (ExacTrac) and SpineLab Planar Fiducial (SPF). During radiosurgery the radiation beam is preferably turned on/off or xe2x80x9cgatedxe2x80x9d as a function of the respiratory cycle, in order to take into account natural fluctuations in a patient""s position that occur during respiration.